In the Service of the Romans
The Thin Prefect's Gronckle is in the service of the Romans. How he got to that position is unknown and it is unknown if he works for them willingly or under duress. He appears to be able to move around unsupervised and is not caged as most other dragons at Fort Sinister. He is also a bit of a guinea pig for the Thin Prefect.
The Thin Prefect has acquired a torn half of Hiccup's notebook, How to Speak Dragonese and attempts to learn Dragonese from it, so he can command a dragon army. He orders about his Gronckle. The Thin Prefect's Gronckle carries out his orders, but the Thin Prefect mostly says the wrong things.
|“||Alvin turned to the Gronckle. "Sit on me!" he ordered in his extremely poor Dragonese. "And put me in the toilet with the other Heirs!"''||”|
|— Book 3|
The Thin Prefect's Gronckle - under the incorrectly stated orders of the Thin Prefect - bites a Roman Soldier's leg, sits on the Thin Prefect, and tosses him into a toilet-tub. When the Thin Prefect finally orders the Gronckle to take Hiccup and Fishlegs to the prison tower, Hiccup has to intervene.
The Thin Prefect's Gronckle is a particularly large specimen for his species, and thick and warty as Gronckles are.
|“||At the Prefect's feet lay a particularly large Gronckle, a dragon about two meters high with a spiny ruff around its neck. When they came into the room it heaved its enormous bulk onto its thick muscly legs and an ominous growling began deep in its thick bull neck.||”|
|— Book 3|
|"How to Train Your Dragon":||Absent||"How to Ride a Dragon's Storm":||Absent|
|"How to Be a Pirate":||Absent||"How to Break a Dragon's Heart":||Absent|
|"How to Speak Dragonese":||Appears||"How to Steal a Dragon's Sword":||Absent|
|"How to Cheat a Dragon's Curse":||Absent||"How to Seize a Dragon's Jewel":||Absent|
|"How to Twist a Dragon's Tale":||Absent||"How to Betray a Dragon's Hero":||Absent|
|"A Hero's Guide to Deadly Dragons":||Absent||"How to Fight a Dragon's Fury":||Absent|
- The Thin Prefect's Gronckle is at various times referred to as "it" and "he".